Method and apparatus for separating aromatic hydrocarbons in an isothermal system

ABSTRACT

An isothermal method is provided for separating aromatic hydrocarbons from a feed stream. The method includes flowing the feed stream through a first channel within a first wafer assembly that contains a rib member. Next, the feed stream is exposed to a first thin film polymer membrane. A stream permeates through the first thin film polymer membrane into a permeate zone. The permeate zone is heated via a heated fluid contained within the rib member. The permeate is produced from the first wafer assembly. The method may include having a plurality of tandem wafer assemblies arranged in series. An apparatus for separating aromatic components from a feed stream is also disclosed. In the preferred embodiment, the apparatus includes a series of tandem wafer assemblies specifically adapted for blending a transportation fuel.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims benefit of U.S. provisional patentapplication Ser. No. 60/523,131 filed Nov. 18, 2003.

FIELD OF THE INVENTION

This invention relates to an apparatus and process for separation ofaromatics from a feed stream. More particularly, but not by way oflimitation, this invention relates to an apparatus and process forseparation of aromatics from gasolines, naphthas, diesel fuels, etc.,with the separation occurring via a membrane member in an isothermalsystem.

BACKGROUND OF THE INVENTION

Membrane based separation processes such as reverse osmosis,pervaporation and perstraction are conventional. The pervaporationprocess is a technique of separation of liquid mixtures. A low-pressurevacuum is maintained on one side of the membrane media to provide a lowenergy approach to vaporizing liquid materials. The vaporizationtemperature of these liquid materials under vacuum conditions is lowerthan the temperature needed at elevated pressures. The liquid mixturesto be separated are conducted onto an upstream side of a membrane, whichis essentially impervious to some of the liquid components but willpermit selective passage of other components in a controlled manneracross the membrane to its downstream side. The membrane is thin, andits perimeter is sealed against fluid traversing the membrane fromupstream to downstream (or vice versa) by some other path than membranepermeation. The downstream side of the membrane is usually exposed to avacuum and the feed stream component(s) permeating through the membranecan be removed in the vapor phase and condensed in a condenser.

In the pervaporation process, a desired feed component, e.g., thearomatic component, of a mixed liquid feed is preferentially dissolvedinto the membrane film. For membranes selective for the desiredcomponent, the desired component is preferentially adsorbed by themembrane. A membrane is exposed at one side to a stream of the mixtureand a vacuum is applied to the membrane at the opposite side so that theliquid compound adsorbed migrates through the membrane via thewell-known solution-diffusion mechanism. Accordingly, the desiredcomponent passes through the membrane and is removed as vapor from itsdownstream side, thereby providing room for the additional adsorption ofthe desired component on the upstream side of the membrane. Aconcentration gradient driving force is therefore established toselectively pass the desired components through the membrane from theupstream side to the downstream side.

Various membranes have been used in the prior art. For instance, U.S.Pat. No. 4,861,628, and U.S. Pat. No. 5,030,355 describe separatingaromatics from non-aromatics such as naphtha, heavy catalytic naphtha(HCN), etc., by for example pervaporation using a suspension-coatedmembrane. The membrane is formed by depositing a polymer on a poroussupport layer, which is a fine dispersion or suspension and not a solidmass.

Among the conventional apparatus used with the pervaporation techniquesare membranes used with spiral-wound and plate frames. For instance, inU.S. Pat. No. 3,398,091 covering a membrane separation using a cellcomprised of a stack of basic units between a pair of end plates isdisclosed. The semi-permeable membranes are held by spacers and asupport. Heat transfer fluid is conducted via an inlet, conduit system,heating compartments and across heat transfer sheets. In conventionalspiral-wound element systems, there can be a significant temperaturegradient across the elements due to this heat load. This can adverselyaffect both the quality and economics of the separation process usingthe pervaporation of fluids. Also, in spiral wound elements, aconcentration gradient is established as a function of the length of thewindings. This can adversely impact the separation performance.Furthermore, there are pressure drop issues and thin film boundary layerissues that adversely influence the local pressure gradient across themembrane surface in spiral wound elements.

Prior art pervaporation processes have used discrete equipment steps toachieve the desired separation. Interconnection of these equipmentdevices for large flow rate applications is expensive. Also, the priorart spiral-wound elements are expensive and difficult to manufacture forhigh temperature services. The majority of commercial spiral-woundelement designs are limited to the 100-120 degree temperature range. Toachieve separations of gasolines, naphthas, diesel fuels and higherboiling hydrocarbons usually higher temperatures are needed in excess of120° C. There therefore is a need for an apparatus and process to applypervaporation of fluids to hydrocarbon materials, especially those usedas transportation fuels, to achieve separation of specific moleculartypes in an economical and efficient fashion.

It is conventional to heat membranes, including polymeric membranes, inorder to increase the membrane's permeability. Some of the difficultiesinvolved in heating of prior art membranes and membrane assembliesinclude adhesive failure in spiral-wound prior art membranes leading tode-lamination and the thermal gradients present when heatingconventional plate-frame membrane assemblies resulting in non-isothermalheating of the membrane itself.

There is therefore a need for polymeric membrane assemblies and polymermembrane separation methods that would provide for heating the polymermembrane to improve permeability.

SUMMARY OF THE INVENTION

In an embodiment, the invention relates to a polymeric membrane waferassembly and a method for using such an assembly for liquid separations.The polymeric membrane wafer assembly (also referred to herein as a“wafer assembly”) comprises a thin film polymer membrane, called a“membrane”, and a frame, called a “wafer”, for supporting the membranewhile interfering as little as practical with membrane permeation. Thethin film polymer membrane comprises polymer selective for permeation ofa desired component or species in a feed stream across the membrane inresponse to a pressure gradient, concentration gradient, etc. Suchmembranes are compatible with pervaporation and perstraction separation.Thin film polymer membrane geometry is conventional and comprises afirst (or “upstream”) side and a second (or “downstream”) side, thefirst and second sides being continuously joined along their perimeterto form a thin member. The wafer comprises a perimeter region forsealing the membrane perimeter against fluid flow and at least one ribfor supporting a side of the thin film polymer membrane away from themembrane perimeter. In an embodiment, one or more distribution weirs areused in the wafer assembly for distributing a feed stream in thevicinity of the thin film polymer membrane. Mesh screens may also beused, generally to provide for turbulent flow in the vicinity of themembrane. A wafer assembly may contain a membrane support fabricpositioned, preferably, on the upstream side of the polymer membrane. Inan embodiment, a rib member may be solid or have a bore therethrough.The method includes allowing a fluid to enter the bore of the rib memberand heating the feed stream as the feed stream is being conductedthrough the wafer assembly. When a plurality of wafer assemblies areused, all or fewer than all of the wafer assemblies can contain suchweirs, screens, support fabrics, and rib members, alone and incombination.

In a preferred embodiment, the thin film polymer membrane is mounted ona membrane support fabric such as Teflon, polyester, nylon, Nomex,Kevlar, etc., and further comprises (i) a porous metallic and/or porousceramic support material abutting the membrane support fabric and (ii) amesh screen, which may be used alone or in combination. Ceramic supportmaterial is preferred and, in the most preferred embodiment, is selectedfrom the group consisting of Cordierite, Aluminum oxide, ZirconiumOxide, Mullite, Porcelain, Stealite and Silicon Nitride and specialcombinations of these. When fabric, porous support material, and screensare used, it should be understood that the ribs could support the thinfilm polymer membrane directly, or alternatively, indirectly via thefabric, porous support material, and/or screen.

In a preferred embodiment, the membranes are cast on to a thin supportof polymeric material, such as TEFLON. The membrane/support subassemblypreferably is in contact with a first side of a thin metallic screen,such as a stainless steel screen. The perimeter of the membrane/supportis held taut against the screen by applying radial tension towards theperimeter of the membrane and then, without releasing the tension,applying a compression force at the perimeter with an O-ring, forexample, to hold the perimeter in position and the membrane taut. Whenthe optional screen and support are used, the permeate side of themembrane is typically in contact with the optional screen and support.The retentate side of the membrane is preferably supported on heatedribs in the membrane assembly in order to heat the membraneisothermally.

In another embodiment, there is provided a method for separating desiredcomponents from a liquid feed stream, and particularly for separatingaromatic hydrocarbons from a liquid feedstream comprising aromatic andnon-aromatic hydrocarbons. The method comprises conducting the feedstream into a retentate zone within a first wafer assembly comprisingthe retentate zone, and a permeate zone, with a dynamic membranesituated therebetween. The feed stream in the retentate zone is in fluidcontact with an upstream side of the first thin film polymer membrane.Process conditions, such as pressure and the relative concentration ofthe feed stream components are regulated to cause a desired componentpresent in the feed stream, such as the aromatic component, to permeatethrough the membrane from the upstream side to a downstream side of thefirst thin film polymer membrane. For example, suctioning can be used toprovide a pressure less than atmospheric pressure on the permeate sideof the membrane. When the retentate side is at a higher pressure, adifferential pressure is established across the membrane, leading topermeation across the membrane from upstream to downstream. Feedstreampressurization and permeate suctioning can be used to provide thepressure gradient, either alone or in combination. When feedstreampressurization is used, the feedstream may be in the vapor, liquid, orliquid-vapor regions of the feedstream phase diagram. When suctioning isused to provide a lower pressure in the permeate zone, the downstreamside of the membrane produces a permeate vapor into the permeate zone,which can be condensed into liquid permeate. Accordingly, the downstreamside of the first thin film polymer membrane is in fluid (includinggaseous) contact with the permeate zone. The permeate in the permeatezone may be in the vapor state, and may be subsequently condensed into aliquid. The permeate can be conducted away from the permeate zone, andcan be conducted away in either the liquid or vapor state. A retentatestream, which can be lean in the desired feedstream component can beconducted away from the retentate zone.

A plurality of wafer assemblies, each containing at least one polymermembrane, can be used in combination. For example, wafer assemblies canbe arranged in parallel, series, and series-parallel fluid flowcircuits. In a preferred embodiment, all or a portion of the retentateis conducted away from the first wafer assembly to a second waferassembly arranged in a parallel fluid-flow configuration with the firstwafer assembly. The feed stream is conducted to a retentate zone in thesecond wafer assembly, and process conditions are regulated to cause asecond desired feed stream component, that may be the same as the firstdesired feed stream component, from an upstream end of a second thinfilm polymer membrane, to the membrane downstream side, and into asecond permeate zone. A second permeate, that may be the same as thefirst permeate, can be conducted away from the second permeate zone. Allor a portion of second permeate conducted away from the second permeatezone can be combined with all or a portion of first permeate conductedaway from the first permeate zone. A permeate stream is created thatpermeates through the second thin film polymer membrane, and into thepermeate zone.

When two or more wafer assemblies are employed in parallel for feedstream separation a differential pressure can be established across thewafer assemblies to provide a driver for membrane permeation. In suchcases, he permeate stream from the plurality of wafer assemblies can beproduced by a suction driving force via the common central outlet tube.Vacuum pumping, vacuum ejecting, and condensation of the permeate vaporssuitable for providing such a pressure differential. Permeate can besuctioned off from the permeate zone via an outlet tube via the commoncentral outlet tube, and subsequently condensed, if desired.

In another embodiment, a wafer assembly's permeate zone is heated with ahot media selected from the group consisting of steam heat, hot gas, hotoil or hot liquids. When a plurality of wafer assemblies are employed,all or fewer than all can employ permeate zone heating.

In another embodiment, there is provided an apparatus for separatingaromatics from a feed stream. The apparatus comprises a first waferassembly that includes a first, second and third wafer. The first waferhas a first and second side along with an outer rim. The second wafer isoperatively attached with the first wafer, with the second wafer havinga first side and a second side and an outer rim. The first wafer andsecond wafer form a first cavity area. The third wafer is operativelyattached with the second wafer, with the third wafer having a first sideand a second side and an outer rim, and wherein the second wafer and thethird wafer form a second cavity area. The first and third wafers maycontain underflow distribution weirs. The second wafer contains apermeate zone.

The apparatus further comprises a first and a second membrane member,where a membrane member comprises an independently selected thin filmpolymer membrane mounted on a membrane support fabric such as Teflon,polyester, nylon, Nomex, Kevlar, etc., and optionally, (i) a porousmetallic and/or porous ceramic support material abutting the membranesupport fabric and (ii) a mesh screen. The ceramic support material ispreferred and, in the most preferred embodiment, is at least one ofCordierite, Aluminum oxide, Zirconium Oxide, Mullite, Porcelain,Stealite and Silicon Nitride. In the most preferred embodiment, thepowdered layer of adsorption media is selected from the group consistingof activated carbon, molecular sieves, zeolites, silica gels, alumina orother commercially available adsorbents, etc. The first membrane memberis disposed within the first cavity so that a first retentate area isformed therein and the second membrane is disposed within the secondcavity so that a second retentate area is formed therein.

A seal means for sealing the wafer assemblies is also included. The sealmeans may comprise a gasket fitted between the first and second waferand an O-ring positioned within a groove on the second wafer.

Other embodiments of seal means may be used. For instance, the sealmeans may comprise a first O-ring fitted about the outer rim in a grooveon the first wafer, and a cooperating second O-ring fitted about theouter rim in a groove on the second wafer. In another embodiment, theseal means comprises double O-rings fitted about the outer rim in a pairof grooves on the first wafer and a cooperating pair of double O-ringsfitted about the outer rim in a pair of grooves on the second wafer. Inyet another embodiment, the seal means for the second and third waferscomprises a first O-ring fitted about the outer rim in a groove on thesecond wafer, and a cooperating second O-ring fitted about the outer rimin a groove on the third wafer. In still yet another embodiment, theseal means comprises double O-rings fitted about the outer rim in a pairof grooves on the second wafer and a cooperating pair of double O-ringsfitted about the outer rim in a pair of grooves on the third wafer.

The apparatus may include a first feed tube disposed through the firstwafer assembly, with the first feed tube delivering a feed stream to thewafer assembly. A first permeate tube is disposed through the firstwafer assembly, with the first permeate tube delivering a producedpermeate from the permeate zone of the first wafer assembly.

In another embodiment, the apparatus further comprises a tandem secondwafer assembly that contains a fourth, fifth, and sixth wafer. Thefourth wafer has a first side and a second side. The fifth wafer isoperatively attached with the fourth wafer, with the fifth wafer havinga first side and a second side, and wherein the fourth wafer and thefifth wafer form a third cavity area. The sixth wafer is operativelyattached with the fifth wafer, the sixth wafer having a first side and asecond side, and wherein the fifth wafer and the sixth wafer form afourth cavity area. The fourth and sixth wafer may contain underflowdistribution weirs.

The assembly further comprises a redistribution tube disposed throughthe first and second wafer assembly, for conducting at least a portionof the retentate from the first wafer assembly to the second waferassembly. Third and fourth membrane members are mounted within the thirdand fourth cavity, respectively.

Additionally, in the preferred embodiment, the first and second waferassembly is arranged in tandem thereby forming an assembly in acylindrical geometry. The geometry is not limited to a circular cylindergeometry. Cylindrical forms based on semicircular, triangular,rectangular, and regular and irregular polygon cross sections may alsobe employed. The tandem wafer assemblies can then be arranged in aseries of tandem wafer assemblies. The number of tandem wafer assembliesarranged in the series depends on design criteria such as flow capacity.

While not wishing to be bound by any theory or model, it is believedthat it is advantageous to configure the wafer assemblies in a modular“wagon wheel” geometry that can be close-coupled with process heatingand cooling zones in close proximity to the membrane surface where thepervaporation of fluids is occurring. Such a geometry would beadvantageous because (1) that the entire assembly is contained within asingle pressure vessel, (2) the assembly can be close-coupled to avacuum system (e.g. vacuum pump) to achieve a highly integrated, compactequipment size, and (3) integration of process heating/re-heating withseparation enhances the overall pervaporation of fluids. In thepervaporation of fluids, the heat load across the membrane separationlayer is a variable depending on the permeate material and operatingconditions (volume, heat of vaporization, vapor pressure versusoperating pressure, etc).

While not wishing to be bound by any theory or model, it is alsobelieved that the instant wafer assembly provides controllable re-heatflexibility, in a zone-by-zone sequence that is close coupled to themembrane surface where the pervaporation is occurring, e.g., by heatingthe wafer ribs. This creates a more isothermal system, where theeffective permeation temperature can be more precisely controlled. Thebulk phase molecular concentrations are also more uniformly controlledwhich enhances the overall separation performance. The preferredembodiment to achieve this isothermal performance is to use steam as theheating fluid. As the various zones in the membrane system array requireheat, steam can rapidly condense locally to provide rapid heating of themembrane and permeate.

Accordingly, hot gas such as steam, or low value stack gas is used asthe preferred heating media. In an embodiment, the hot gas flows throughthe wafer assemblies via the ribs and provide the necessary heat inputto the system. In an embodiment, an alternative heater assembly, e.g., aserpentine coil tubular design with or without external fins is attachedto the membrane wafers. The design of the finned tube heating elementscan be adapted to accommodate additional hydrodynamic and heat transferconsiderations and the design of the fins will also accommodateadditional hydrodynamic considerations similar to the design of staticmixer elements. In this embodiment, additional fluid mixing and flowturbulence favorably influence the thin film boundary layer on thehigh-pressure side of the membrane surface to enhance flux andselectivity by avoiding hydrodynamic static zones.

The cylindrical tandem wafer assemblies set forth herein are consistentwith plant modular equipment scales typically found in the petrochemicalindustry. The cylindrical tandem wafer assemblies, which resemble a“wagon wheel” geometry, are scalable and can be made in either large orsmall sizes. An example of a small size device would be onboardautomobile fuel separation devices.

In an embodiment, the thin film polymer membrane further comprises athin film adsorption material in contact with the upstream side of themembrane, which may be in the form of a fmely dispersed powder, bondedto a subsequent layer or a material that has been fmely dispersed andcross-linked to form a porous layer within the membrane film. Techniquessuch as thin film coating, controlled pyrolisis, thermal treating,plasma coating, etc, can be used to achieve this functionality. Theadsorptive layer enhances the local concentration gradient of the targetmolecules. The thin film adsorbent and membrane film are both selectivefor the target molecule. The layered, porous system allows the targetmolecule's concentration gradient (pressure gradient, etc.) to becontrolled to enhance separation performance. In one of the preferredembodiments, the thin film adsorbent is selected from the groupconsisting of activated carbon, molecular sieves, zeolites, silica gels,alumina or other commercially available adsorbents, etc.

In another embodiment, pressure and temperature swing process control,and combinations thereof, can be used in connection with the adsorptionmedia. In a pressure swing mode, the adsorption media sees a highpressure and low-pressure (vacuum) gradient. In the high-pressure zone,the target molecules are attracted to the media from the bulk fluidphase. As these target molecules migrate to the low-pressure zone, theydesorb into bulk fluid phase on the low-pressure side.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of the first outer wafer.

FIG. 1B is a side elevation view of the first wafer of FIG. 1A.

FIG. 1C is a perspective view of the first outer wafer of FIG. 1A fromthe opposite plane.

FIG. 2A is a perspective view of the internal wafer.

FIG. 2B is a side elevation view of the internal wafer of FIG. 2A.

FIG. 2C is a cross-sectional view of the internal wafer of FIG. 2A takenfrom line 2C-2C.

FIG. 3A is a perspective view of the second outer wafer.

FIG. 3B is a side elevation view of the second outer wafer of FIG. 3A.

FIG. 3C is a perspective view of the first outer wafer of FIG. 1A fromthe opposite plane.

FIG. 4 is an exploded side elevation view of the two wafer assemblies.

FIG. 5A is an exploded side elevation view of the two wafer assembliesseen in FIG. 4 detailing one embodiment of the membrane member.

FIG. 5B is an exploded side elevation view of the two wafer assembliesseen in FIG. 4 detailing a second embodiment of the membrane member.

FIG. 5C is a schematic of the flow through the second embodiment seen inFIG. 5B.

FIG. 6 is a plan view of two internal wafers in tandem.

FIG. 7A is a schematic side elevation view of tandem wafer assembliesarranged in series.

FIG. 7B is a schematic front view of one of the tandem wafer assembliesseen in FIG. 7A.

FIG. 8 is a-perspective view of tandem wafer assemblies arranged inseries along with the tubing members.

FIG. 9 is a partial cut away view of the tandem wafer assemblies seen inFIG. 8.

FIG. 10 is a cross-sectional view taken from line 10-10 in FIG. 6 of thepreferred embodiment of the flow pattern through tandem waferassemblies.

FIG. 11A shows a first embodiment of a seal member for the waferassembly.

FIG. 11B shows a second embodiment of a seal member for the waferassembly.

FIG. 11C shows a third embodiment of a seal member for the waferassembly.

FIG. 12 shows the operating envelope for a preferred membrane separationsystem. Conventional membrane separations would occur along the linedepicted by diamond points. As shown, temperature and pressure woulddecrease across the membrane from the feed zone to the permeate zone forconventional membranes. For membrane separations of the invention,however, the separations can be conducted isothermally or withincreasing temperature (“heating operation”) from the feed zone to thepermeate zone, as shown.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention relates to thin film polymeric membrane wafer assemblies,and the use of such wafer assemblies for separating desired species orcomponents from liquid feedstreams.

As discussed, A membrane wafer assembly comprises a thin film polymermembrane and a frame, called a “wafer”, for supporting the thin filmpolymer membrane while interfering as little as practical with membranepermeation. The thin film polymer membrane comprises polymer selectivefor permeation of a desired component or species in a feed stream acrossthe membrane in response to a pressure gradient, concentration gradient,etc.

Polymer used in a thin film polymer membrane within a wafer assemblyshould be selective for permeation of a desired feedstream component.Should it be desired to permeate different feedstream components acrossindividual wafer assemblies in an arrangement of one or more suchassemblies, the wafer assemblies can contain membranes comprisingindependently selected polymers. Additionally, in one of the preferredembodiments, the polymer membrane is independently selected frompolymers useful for selective permeation of aromatic species. When asecond polymer membrane is used, its polymer can be independentlyselected. Mixtures of polymers can be used in the membranes. The term“polymer” is to be used in the general sense of macromolecular, andincludes, for example, homopolymers, copolymers, terpolymers,prepolymers, and oligomers.

In cases where it is desirable to separate aromatics from a feed streamcontaining an aromatic component, a polymer capable of selectivelypermeating aromatics can be used. Examples of polymers suitable foraromatic/non-aromatic separations of liquid hydrocarbons can be found inthe following United States patents: U.S. Pat. No. 4,944,880 coveringpolyimide/aliphatic polyester copolymers, U.S. Pat. No. 4,946,594covering crosslinked copolymers of aliphatic polyester diols anddianhydride, U.S. Pat. No. 5,093,003 covering halogenated polyurethanes,U.S. Pat. No. 5,550,199 covering diepoxide crosslinked/esterifiedpolyimide-aliphatic polyester copolymers, U.S. Pat. No. 4,990,275covering polyimide aliphatic polyester copolymers, U.S. Pat. No.5,098,570 covering multi-block polymer comprising a urea prepolymerchain extended with a compatible second prepolymer, the membrane madetherefrom and its use in separations, U.S. Pat. No. 5,109,666 coveringpolycarbonate membranes for separations of aromatics from saturates,U.S. Pat. No. 4,828,773 covering highly aromatic anisotropicpolyurea/urethane membranes and their use for the separation ofaromatics from non-aromatics, U.S. Pat. No. 4,837,054 covering thin filmcomposite membrane prepared by deposition from a solution, U.S. Pat. No.4,861,628 covering thin film composite membrane prepared by suspensiondeposition, U.S. Pat. No. 4,879,044 covering highly aromatic anisotropicpolyurea/urethane membranes and their use for the separation ofaromatics from non-aromatics, U.S. Pat. No. 4,914,064 covering highlyaromatic polyurea/urethane membranes and their use for the separation ofaromatics from non-aromatics, U.S. Pat. No. 4,921,611 covering thin filmcomposite membrane prepared by deposition from a solution, U.S. Pat. No.4,929,357 covering Isocyanurate crosslinked polyurethane membranes andtheir use for the separation of aromatics from non-aromatics, U.S. Pat.No. 4,983,338 covering isocyanerate crosslinked polyurethane membranesand their use for the separation of aromatics from non-aromatics, U.S.Pat. No. 5,030,355 covering thin film composite membrane prepared bysuspension deposition, U.S. Pat. No. 5,039,417 covering membrane madefrom a multi-block polymer comprising and imide or amide-acid prepolymerchain extended with a compatible second prepolymer and its use inseparations, U.S. Pat. No. 5,039,418 covering membrane made from amulti-block polymer comprising an oxazolidone prepolymer chain extendedwith a compatible second prepolymer and its use in separations, U.S.Pat. No. 5,039,422 covering multi-block polymer comprising a ureaprepolymer chain extended with a compatible second prepolymer, themembrane made therefrom and its use in separations, U.S. Pat. No.5,049,281 covering multi-block polymer comprising of first prepolymermade by combining epoxy with diamine, chain extended with a compatiblesecond prepolymer, the membrane made therefrom and its use inseparations, U.S. Pat. No. 5,055,632 highly aromatic polyurea/urethanemembrane and their use for the separation of aromatics fromnon-aromatics, U.S. Pat. No. 5,063,186 covering highly aromaticpolyurea/urethane membranes and their use of the separation of aromaticsfrom non-aromatics, U.S. Pat. No. 5,075,006 covering isocyanerratecrosslinked polyurethane membranes and their use for the separation ofaromatics from non-aromatics, U.S. Pat. No. 5,096,592 coveringmulti-block polymer comprising on ester prepolymer, chain extended witha compatible second prepolymer, the membrane made therefrom and its usein separations, U.S. Pat. No. 5,098,570 covering multi-block polymercomprising a urea prepolymer chain extended with a compatible secondprepolymer, the membrane made therefrom and its use in separations, U.S.Pat. No. 5,130,017 covering multi-block polymer comprising a first amideacid prepolymer, chain extended with a compatible second prepolymer, themembrane made therefrom and its use in separations, U.S. Pat. No.5,221,481 covering multi-block polymer comprising an ester prepolymer,made by combining epoxy with polyester chain extended with a compatiblesecond prepolymer, the membrane made therefrom and its use forseparations, U.S. Pat. No. 5,290,452 covering crosslinked polyesteramide membranes and their use for organic separations, U.S. Pat. No.5,028,685 covering halogenated polyurethanes, U.S. Pat. No. 5,128,439covering saturated polyesters and crosslinked membranes therefrom foraromatic/saturate separations, U.S. Pat. No. 5,138,023 coveringunsaturated polyesters and crosslinked membranes therefrom foraromatic/saturate separation, U.S. Pat. No. 5,241,039 coveringpolyimide/aliphatic polyester copolymers without pendent carboxylic acidgroups, U.S. Pat. No. 5,012,035 covering polyphthalate carbonatemembranes for aromatic/saturates separation, U.S. Pat. No. 5,012,036covering polyarylate membranes for aromatic/saturates separations, U.S.Pat. No. 5,177,296 covering saturated polyesters and crosslinkedmembranes therefrom for aromatics/saturates separation, U.S. Pat. No.5,180,496 covering unsaturated polyesters and crosslinked membranestherefrom for aromatics/saturates separation, U.S. Pat. No. 5,107,058covering olefin/paraffin separation via membrane extraction, U.S. Pat.No. 5,107,059 covering iso/normal paraffin separation by membraneextraction. Other suitable polymers include polyacrylonitrile (“PAN”)and polysulfone (“PS”). In an embodiment, PVA and PS membranes aresupported on a non-woven polymer support, such as porous polyester. Thin(e.g., 0.01 micrometer to 10 micrometer) polymer layers can be used toenhance selectivity. For example, thin layers of polyvinyl alcohol(“PVA”), polydimethylsiloxane (“PDMS”), and cellulose esters can beused.

A thin film polymer membrane wafer assembly comprises a thin filmpolymer membrane and at least one wafer. The wafer will now be describedin terms of particular embodiments relating to the separation ofaromatics from a liquid feed containing aromatic and non-aromaticcomponents, as shown in the figures. It should be noted that theinvention is not limited to such embodiments.

A wafer suitable for use in an embodiment is set forth in FIG. 1A. Morethan one wafer can be employed in a wafer assembly. While the wafer isshown in the geometry of a thin semicircular cylinder, it should beunderstood that other cylindrical geometries are suitable; for example,cylinder having a cross sections such as circular, triangular,rectangular, regular polygon, and irregular polygon cross sections canbe used. Referring now to FIG. 1A, a perspective view of the first outerwafer 2 a will now be described. The first outer wafer 2 a is generallya semicircular solid member. The first outer wafer contains asemicircular outer edge 4 that extends to the radial surface 6. Thesemicircular outer edge 4 contains a rim 8, with the rim 8 having aplurality of openings, as seen for instance at 10, for placement offasteners such as screws, or O-ring grooves which are not shown in thisfigure. The semicircular outer edge 4 contains a first indentation 12 atthe top portion (also referred to as the apex) of the wafer 2 a. Theindentation 12 is configured to receive a tubular member, as describedbelow.

The wafer 2 a also contains a first corner indentation 14 and a secondcorner indentation 16, with the corner indentations 14, 16 beingconfigured to also receive tubular members. The radial surface containsa first side indentation 18 and a second side indentation 20, along witha center indentation 22, which is configured to receive and beoperatively associated with a tubular member. The functions of thetubular members are different and is more fully set forth below. Asdiscussed, the wafer 2 a has a solid back wall 24. In other words, thewafer 2 a is in the form of a plate. The back wall 24 has two underflowweirs that traverse it, namely underflow weir 26 and underflow weir 28.The weirs 26, 28 are raised projections that will alter the flow patternof the feed stream as will be more fully set out below. The weirs 26, 28also add to the structural support of the wafer 2 a. For larger diametersystems, additional ribs and indentations for tubular members can beprovided.

FIG. 1B is a side elevation view of the first wafer 2 a of FIG. 1A. Itshould be noted that like numbers appearing in the various figures referto like components. Thus, the radial surface 6 is shown along with theindentations 14, 18, 22, 20, and 16. FIG. 1B also depicts the rim 8 thatextends to the back wall 24. Also shown are the redistribution holes 30a, 30 b. Referring to FIG. 1C, a perspective view of the first outerwafer of FIG. 1A from the opposite plane is shown. FIG. 1C depicts theback wall 24.

Referring now to FIG. 2A, a perspective view of the internal wafer 34 awill now be described. The internal wafer 34 a is also a semicircularcontour 36 and has an upper outer rim 36 a that has containedtherethrough openings, such as the opening 38, for placement of fastenermeans such as screws, or O-ring grooves, which are not shown in thisfigure. The internal wafer 34 a has a first rib member 40 and a secondrib member 42. The ribs 40,42 have bored holes 44, 46 there through. Thebored holes 44, 46 will allow a hot media, such as steam, to flowthrough the ribs thereby heating the contents of the wafer assembly, aswill be more fully explained below. For larger diameter systems,additional ribs and indentations for tubular members can be provided.

The internal wafer 34 a has a top indentation 48, at the apex, forplacement of a tubular member. The outer rim 36 a extends to theradially flat surface 50. The radially flat surface 50 will have a firstcorner indentation 52 and a second corner indentation 54; additionally afirst side indentation 56 and a second side indentation 58 is included.The center indentation 60 is shown with the aperture 62 there through.The internal wafer 34 a does not contain a wall, but instead has openareas. Therefore, the numerals 64, 66, and 68 seen in FIG. 2A representopen areas which correspond to the permeate zone. The internal wafer 34a has a first ledge 72 a and a second ledge 74 a.

The side elevation view of the internal wafer 34 a of FIG. 2A will nowbe described with reference to FIG. 2B. The radially flat surface 50 isshown along with the aperture 62. The outer rim contains the upper rimsurface 36 a and the lower rim surface 36 b and wherein both rimsurfaces 36 a, 36 b will serve as sealing surfaces as will be describedin greater detail below. As seen in FIG. 2C, upper rim surface 36 aleads to a first ledge 72 a and second ledge 74 a while lower rimsurface 36 b leads to third ledge 72 b and fourth ledge 74 b.

Referring now to FIG. 3A, a perspective view of the second outer wafer76 a. In the preferred embodiment, the second outer wafer 76 a isgenerally the same structurally as the first outer wafer 2 a. Thus,second outer wafer 76 a contains a semicircular outer edge 78 thatextends to the radial surface 80. The semicircular outer edge 78 andradial surface 80 contains a rim 82, with the rim 82 having a pluralityof openings, for instance as seen at 84, for placement of fasteners suchas screws, or may contain O-ring grooves which are not shown in thisfigure. The semicircular outer edge 78 contains a first indentation 86at the top portion (also referred to as the apex) of the wafer 76 a. Theindentation 86 is configured to receive a tubular member, as will bemore fully set forth below. The functions of the tubular members aredifferent and will be more fully set forth below.

The wafer 76 a also contains a first corner indentation 88 and a secondcorner indentation 90, with the corner indentations 88, 90 beingconfigured to also receive tubular members. The radial surface 80contains a first side indentation 92 and a second side indentation 94,along with a center indentation 96, which is configured to receive andbe operatively associated with a tubular member.

The wafer 76 a has a solid back wall 98. In other words, the wafer 76 ais in the form of a plate. The back wall 98 has two underflow weirs thattraverse it, namely underflow weir 100 and underflow weir 102. The weirs100, 102 are raised projections that will alter the flow pattern of thefeed stream as will be more fully set out below. The weirs 100, 102 alsoadd to the structural support of the wafer 76 a. For larger diametersystems, additional ribs and indentations for tubular members can beprovided.

FIG. 3B is a side elevation view of the first wafer 76 a of FIG. 3A. Asnoted earlier, like numbers appearing in the various figures refer tolike components. Thus, the radial surface 80 is shown along with theindentations 88, 94, 96, 92, and 90. The indentation 92 has aredistribution aperture 104. The indentation 94 has redistributionaperture 105. FIG. 3C is a perspective view of the second outer wafer ofFIG. 3A from the opposite plane, with this view depicting the solid backwall 98 as well as supports 99 a and 99 b.

Referring now to FIG. 4, an exploded side elevation view of the firstwafer assembly 106 in tandem with a second wafer assembly 108 will nowbe described. As seen in FIG. 4, the wafer assembly 106 consists of thefirst outer wafer 2 a, the first membrane member 110, the internal wafer34 a, the second membrane member 112, and then the second outer wafer 76a. Thus, a wafer assembly consists of the first outer wafer, membranemember, internal wafer, membrane member and then the outer wafer. Itshould be noted that the first outer wafer 2 a is of the reinforcedtype, which is thicker and is structurally stronger than wafer 76 a.

As shown in FIG. 4, a second wafer assembly 108 is in tandem with thefirst wafer assembly 106. Thus, the second wafer assembly 108 consistsof the first outer wafer 2 b, the first membrane member 114, theinternal wafer 34 b, the second membrane member 116, and the secondouter wafer 76 b. According to the teachings of the present invention,the first wafer assembly 106 is operatively attached in tandem to thesecond wafer assembly 108 to form tandem wafer assemblies.

A plurality of screws is shown for fastening a wafer assembly together.For instance, screw 117 a fits through opening 117 b in wafer 2 a andscrew 117 c fits through opening 117 d in wafer 76 a with cooperatingopenings 117 e/117 f in wafer 34 a so that wafers 2 a, 34 a and 76 a arefastened together.

FIG. 5A is an exploded side elevation view of the tandem waferassemblies seen in FIG. 4 detailing one embodiment of the membranemember. FIG. 5A depicts the preferred embodiment of the polymericmembrane wafer assembly. In this preferred embodiment, the membranemember 110 that comprises a feed spacer screen 120 a, a gasket 122 a, athin film membrane 124 a and a sintered metal member 126 a. The sinteredmetal member 126 a is typically attached to member 34 a by electron beamwelding. Other forms of attachment common to those skilled in the artare also feasible. The member 126 a may [also] be constructed of aporous metallic or porous ceramic support material. The porous supportmaterials provide an engineered flat surface for the membrane fabric tolay on and are common to both the dynamic and polymeric embodimentsherein disclosed.

The feed spacer screen is commercially available. The feed spacer screenis commercially available metal or non-metallic screen materials. Thesintered metal member 126 a is available from Martin Kurz and Co. Inc.under the name DYNAPORE. Various grades of DYNAPORE may be used fromgrade TWM-80 to BWM-80. DYNAPORE grades made from five (5) layer screenfilter media are the most preferred embodiment for this sintered metalmember. Viton gasket available from DuPont is suitable. Sintered metalavailable from Mott Corporation under the name Sintered Metal issuitable.

The second membrane member 112 comprises a feed spacer screen 128 a, agasket 130 a, a thin film membrane 132 a and a sintered metal 134 a. Thesintered metal member 134 a is typically attached to member 34 a byelectron beam welding. Other forms of attachment common to those skilledin the art are also feasible. The member 134 a may also be a porousmetallic or porous ceramic support material.

The membrane member 114 comprises a feed spacer screen 120 b, a gasket122 b, a thin film membrane 124 b and a sintered metal member 126 b. Thesintered metal member 126 b is typically attached to member 34 a byelectron beam welding. Other forms of attachment common to those skilledin the art are also feasible. In one preferred embodiment, the secondmembrane member 116 comprises a feed spacer screen 128 b, a gasket 130b, a thin film membrane 132 b and a sintered metal member 134 b. Thesintered metal member 134 b is typically attached to member 34 a byelectron beam welding. Other forms of attachment common to those skilledin the art are also feasible. The members 126 a and 134 a may also beconstructed of a porous metallic or porous ceramic material.

It should be noted that different components within the membrane membersare possible. For instance, the membrane support fabric, while not shownin FIG. 5A, may be included as part of the membrane members as depictedin FIG. 5B. The FIG. 5B is discussed below. Additionally, differentsequencing and/or arrangement of the components within the membranemember is also possible.

FIG. 5B is an exploded side elevation view of the tandem waferassemblies seen in FIG. 4 detailing a second embodiment of the membranemember package. The embodiment of FIG. 5B depicts the dynamic membrane,i.e., a membrane coated with a layer of material selective for theadsorption of the component or species selected for membrane permeation.In this second preferred embodiment, the membrane member 400 comprisesO-ring rope 409 a, a wire mesh screen 410 a, a powdered layer ofadsorption media 412 a, membrane 414 a, membrane support fabric 416 a,and O-ring rope 417 a. Also included is a porous support material media418 a, which may be either a porous metallic or porous ceramic supportmaterial abutting the membrane support fabric. The O-ring rope iscommercially available from American Seal Inc. under the name Cabres.The metallic and non-metallic feed spacer screen (410 a) is commerciallyavailable. The membrane support fabric is commercially available from,e.g., W. L. Gore, Inc. under the trademark GoreTex. GoreTex is a Teflonpolyetrafluoroethylen (PTFE) fabric. The membrane support fabric mayalso be polyester, nylon, Nomex or Kevlar type of fabric. Teflon, Nomexand Kevlar are trademarks of DuPont. The porous metallic supportmaterial (418 a) is commercially available from Martin Kurz and Co. Inc.under the name DYNAPORE. Various grades of DYNAPORE may be used fromgrade TWM-80 to BWM-80. DYNAPORE grades made from 5 layer screen filtermedia are the most preferred embodiment for this sintered metal member.The adsorption media may be placed on a porous sheet, or placed onto thesurface of the thin film membrane. Preferably, the adsorption media hasa surface area ranging from about 100 to about 1500 square meters pergram. Typical adsorbent material will be activated carbon, molecularsieves, zeolites, silica gels, alumina. Impregnated adsorbents may alsobe used. Adsorbent materials may be impregnated with the followingmaterials to enhance performance—Sodium, Cobalt, Molybdenum, Copper andother metals. Suitable adsorbent materials are available from, e.g., (a)Calgon Co. for activated carbon and impregnated activated carbon, withthe commercial trade names for non-impregnated being Cal F-200, and CalF-400, and for impregnated is Centur (Sodium impregnated); (b) Grace Co.for molecular sieves/zeolites, silica gels, and the commercial tradenames of molecular sieves/zeolites are 13X, 5A and others, andcommercial trade names of silica gels are Grace Gel and others; (c)ALCOA Co. for Alumina, and the commercial trade names are A-200, A-400and others; and (d) ExxonMobil Co. for Zeolites, with the commercialtrade names being ZSM-5, MCM series and others.

The second membrane member 402 comprises O-ring rope 409 b, a wire meshscreen 410 b, a powdered layer of adsorption media 412 b, membrane 414b, membrane 416 b, O-ring rope 417 b, and a porous support material 418b, that may be either metallic or ceramic.

The membrane member 406 comprises an O-ring rope 409 c, a wire meshscreen 410 c, a powdered layer of adsorption media 412 c, membrane 414c, O-ring rope 417 c, support fabric membrane 416 c, and a poroussupport material 418 c, that may be either metallic or ceramic. In onepreferred embodiment, the second membrane member package 408 comprisesan O-ring rope 409 d, a wire mesh screen 410 d, a powdered layer ofadsorption media 412 d, membrane 414 d, membrane support fabric 416 d,an O-ring rope 417 d, and a porous support material 418 d, that may beeither metallic or ceramic. It should be noted that differentcomponents, or a different sequencing of components, within the membranemembers are possible.

FIG. 5C is a schematic of the flow through the dynamic embodiment seenin FIG. 5B. The flow stream “F” flows through the powder adsorptionmedia, then through the thin film polymeric membrane and then throughthe membrane fabric, and in turn through the porous support.

Referring now to FIG. 6, a plan view of two internal wafers connected intandem is shown. Thus, an internal wafer such as 34 a and a secondinternal wafer 34 b are operatively attached. Several methods ofattachment are possible including bolts/screws 302, 304 aligned externalto tubular members 148 and 149 are the preferred embodiments.Alternative methods could be open rectangular pin or harpsscrewed/bolted into wafers 34 a and 34 b. Compression bands may also beused. Since both wafers 34 a, 34 b are semicircular, the two coupledwafers form a cylindrical assembly with a generally circularcross-section. This cylindrical assembly allows for the entire device tobe placed within a pressure vessel 135, and therefore, maximizes thespace and volume within said vessel 135. In other words, the cylindricalassembly is the most efficient configuration for processing largequantities of feed stream within a pressure vessel, although thecylinder need not be a semi-circular or circular cylinder. The vessel135 may have a hot media, such as steam, placed within the annulus areaA.

FIG. 6 depicts the center indentation 60 a and 60 b which form acylindrical passage for placement of a tubular member 140 for thepermeate, along with the apertures 140 a, and 140 b for passage of thepermeate into tubular member 140. Also, the indentation 48 a has atubular member 142 therein for the inlet feed. The indentation 48 b hasa tubular member 144 therein for the feed (retentate) outlet. Theindentation 52 a and 52 b has a tubular member 146 therein for the steamsupply. The indentation 54 a and 54 b has a tubular member 148 for thesteam supply. The side indentations 56 a, 56 b has a redistributiontubular member 150. The side indentations 58 a, 58 b has aredistribution tubular member 152.

The tubular member 142 will deliver the feed stream into the wafers. Thetubular member 144 will be the outlet tube for the feed stream(retentate). The tubular members 146 and 148 are the supplemental steamsupply inlet. The tubular members 150 and 152 are the redistributiontubes for redistributing the retentate from the area of wafer 34 a tothe area of wafer 34 b, as will be more fully described below.Attachment plates 306, 308 are also used to secure tubular members 144,142.

Referring now to FIG. 7A, a schematic side elevation view of tandemwafer assemblies arranged in series will now be described. FIG. 7Adepicts a wafer assembly that comprises an end wafer 160 attached to aninternal wafer 162 that is attached to an end wafer 164. The end wafer160 has two support projections, namely 166 and 168 for providingstructural support and cooperating with a reciprocal set of supportprojections in a different plane from another wafer assembly. The endwafer 164 has two support projections, namely 170 and 172 for providingstructural support and cooperating with a reciprocal set of supportprojections in a different plane. This wafer assembly is denoted as W1.

The reciprocal wafer assembly in tandem includes an end wafer 174attached to an internal wafer 176 that is attached to an end wafer 178.The end wafer 174 has two support projections, namely 176 and 178 forproviding structural support and cooperating with a reciprocal set ofsupport projections in a different plane. The end wafer 178 has twosupport projections, namely 180 and 182 for providing structural supportand cooperating with a reciprocal set of support projections in adifferent plane. This wafer assembly is denoted as W2.

Wafer assemblies W3 and W4 are shown. The wafer assemblies W3 and W4 areessentially the same as W1 and W2. The wafer assembly W3 will beoperatively attached to the wafer assembly W4. FIG. 7A depicts the flowthrough of the feed stream. More particularly, the feed stream wouldenter as through the arrows designated as 190, 192 via inlet tube 142.Referring to FIG. 7B, a schematic front view tandem wafer assembly W3,W4 will now be described. As seen in FIG. 7B, feed/retentate liquid fromW3 flows out of W3 via redistribution tubes 150 and 152 and enters W4via these tubes 150, 152; the permeate flows out of W3 and W4 and intotubular member 140.

Returning to FIG. 7A, the feed stream exits via the outlet tube 144 asdesignated by the arrows 194, 196. The portion of the feed stream thatpermeates through the membrane members exits via tube 140, which isdenoted by the numerals 198 and 200. As per the teaching of thisinvention, this flow pattern is similar for all wafer assemblies (W1-W2,W5-W6, W7-W8) as shown in FIG. 7A.

FIG. 7A depicts the wafer assembly W5 that will be operatively attachedto wafer assembly W6. Finally, wafer assembly W7 is shown operativelyattached to wafer assembly W8. Wafer assemblies W5 and W6 areessentially the same as W3 and W4, and wafer assemblies W7 and W8 areessentially the same as wafer assemblies W5 and W6 except that in the W7wafer assembly, the end wafer 2 a is the reinforced type, and that inW8, the end wafer 2 b is also the reinforced type. The internal wafers34 a and 34 b, and the outer wafers 76 a, 76 b are also shown.

The FIG. 7A illustrates that the wafers are arranged in tandem, and thenthe tandem wafer assemblies are arranged in series. In other words,wafer W1 is in tandem with wafer W2. By adding the tandem waferassemblies in series, the operator in effect increases the flowcapacities for the apparatus. FIG. 7A also shows how the supportprojections will cooperate with an adjacent support projection on anadjacent wafer but in a different plane. For instance, supportprojections 170 and 172 of the end wafer 164 will abut a back wall 350and wafer projections 206 and 208 of the end wafer 210 will abut theback wall 351 of wafer 164. This adds strength and distributes thecompressive load when the tandem wafer assemblies are compressed intoplace in series.

Referring now to FIG. 8, a perspective view of tandem wafer assembliesarranged in series along with the tubing members will now be described.In this view, the wafer assemblies W1, W2, W3, W4, W5, W6, W7, and W8are shown. It should be noted that the end wafer 2 a of wafer W7 and endwafer 2 b of wafer W8 is of the reinforced type. The feed inlet tubular142 is shown, the permeate tubular 140 is shown, and the feed outlettubular 144 is shown in FIG. 8. The stopper plate 244 and the couplingplate 246 are shown, along with the redistribution tubes 150, 152.

FIG. 9 is a partial cut away view of the tandem wafer assemblies seen inFIG. 8. Thus, the W1, W2, W3, W4, W5, W6, W7, and W8 wafer assembliesare shown. This partial cross-section depicts the redistribution tube152 along with the nozzles 220, 222, 224, 226, 228, 230, 231, 232, 233and 234. These nozzles direct the feed (retentate) from the first waferassembly to the second wafer assembly arranged in tandem. For example,the feed is directed from wafer assembly W1 to wafer assembly W2 vianozzle 224 and nozzle 226. Additionally, permeate tube 140 is shown,along with the nozzles 236, 238, 240, 242 and 243 for directing thepermeate produced from the wafer assemblies from the permeate zone (thepermeate zone 262 is shown in FIG. 10) to the permeate tube 140 which isultimately produced from the apparatus.

In FIG. 9, a first stopper plate 244 is braced together with a couplingplate 246, with the stopper plate 244 and coupling plate 246 being addedin one preferred embodiment to aid in properly compressing the series oftandem wafer assemblies together. A second stopper plate 248 bracedtogether with a coupling plate 250 is shown, with the stopper plate 248and coupling plate 250 being added on the opposite side for thereciprocal compression of the series of tandem wafer assembliestogether. It should be noted that in one preferred embodiment, thecoupling plates are made up of two halves that are attached together,generally by a fastener means such as nuts and bolts. The stopper plates244, 248 are attached also by fastener means such as nuts and bolts tothe wafer assemblies. The stopper plates provide additional mechanicalintegrity to the assembly of wafers W1 through W8.

Referring now to FIG. 10, a cross section view of the preferredembodiment of the flow pattern through a series of tandem waferassemblies will now be described. Thus, there is shown the first outerwafer 2 a that is operatively attached to the internal wafer 34 a. Theinternal wafer 34 a is in turn operatively attached to the second outerwafer 76 a of wafer assembly W7, as previously described. The firstmembrane member 110 is disposed within the first cavity created betweenthe wafer 2 a and the wafer 34 a. The second membrane 112 is disposedwithin the second cavity created between the wafer 76 a and the wafer 34a.

The feed stream will be channeled through the channel 260. The weir 26and weir 28 will cause the feed stream to undergo turbulent flow. Aportion of the stream will react with the membrane 110 and the permeatethus produced will be directed into the permeate zone 262 which in turnis directed to the permeate tubular 140 via the nozzle 243. The permeatepath is shown by arrows “P”. The portion of the feed stream that doesnot permeate through the membrane member 110 is known as the retentate,and this retentate flows through the retentate area that is shown bypath arrows “R”.

In accordance with this embodiment, the incoming feed stream is alsochanneled through the channel 263. The weir 102 and weir 100 will causethe feed stream to undergo turbulent flow. A portion of the stream willreact with the membrane 112 and the permeate thus produced will bedirected to the permeate zone 262 and then into the permeate tubular 140via the nozzle 243. As noted earlier, the permeate flow path is shown bythe arrow P. The portion of the inlet fluid stream that is unreacted (inthe sense that it is lean in the permeated species or component), i.e.,the retentate, flows through the retentate area that is shown by thepath arrow R.

In the preferred embodiment, the retentate from the first wafer assemblyW7 is flown to the tandem wafer assembly W8 via the redistribution tubes150, 152 (tube 150 is not shown in FIG. 10) where it will again beexposed to the similar process in that the feed stream (retentate) willbe exposed to the weirs, and membrane members. The permeate will bedirected to the permeate tubing 140 and the retentate will be directedto the outlet tube 144.

As illustrated in FIG. 10, similar flow patterns are present for alltandem wafer assemblies. More particularly, FIG. 10 also depicts theflow patterns for wafers W5 and W6. The P arrows depict flow for thepermeate path and the R arrows depict flow for the retentate for waferassemblies W5, W6, W7, and W8. For instance, retentate exits wafer W7via nozzle 233, and enters via nozzle 400. Retentate will eventuallyexit wafer W8 via nozzle 402 into outlet tube 144. The permeate willenter permeate tubular 140 via nozzle 404. Additionally, the condenserand vacuum pump 300 which provides the suction to permeate tube 140, andin turn to the permeate zone, is also shown in FIG. 10.

In FIG. 11A, a first embodiment of a seal member for the wafer assemblywill now be described. The seal member shown in FIG. 11A is a gasket 270that is well known in the art. The wafer 2 a contains a rim 272 on itsperimeter, and the internal wafer 34 a contains a reciprocal rim 274 onits perimeter. A screen 276 (which for example may be a component of themembrane member package 110 or of membrane member package 400) is shownconfigured to be positioned within a ledge surface 277 a of the wafer 34a. The thin film membrane is denoted by the numeral 278. Therefore, thegasket 270 is placed between the rims 272 and 274 in order to provide aseal means. The gasket 270 can be Viton (available from DuPont) or otherelastomer suitable for service with the desired feedstream, permeate,retentate, and process conditions.

A second embodiment of a seal member for the wafer assembly is shown inFIG. 11B. In this embodiment, the screen 276 is used with the membranemember denoted by the numeral 280. The gasket 270 is again used. In thisembodiment, a second ledge 282 is configured within the rim 274. AnO-ring 284 is placed within this second ledge and is abutted by thescreen 276. The O-ring 284 will provide a secondary sealing mechanism asit is compressed against the membrane member 280 which in turn iscompressed against the gasket 270.

In FIG. 11C, a third embodiment of a seal member for the wafer assemblyis shown. In this embodiment, the O-ring 284 is again positioned withinthe ledge 282. In the wafer 2 a, two grooves are configured in rim 272,namely, groove 286 and groove 288. An O-ring 290 is placed within groove286 and an O-ring 292 is within groove 288. This embodiment allows theO-ring 290 and the O-ring 284 to cooperate together for a sealing means.The O-ring 292 provides a redundant seal, with the seal occurringbetween the O-ring 292 and the membrane member 280.

The membranes described herein are useful for separating a desiredcomponent or species from a liquid feed. Perstractive and pervaporativeseparation can be used.

In perstractive separation, permeate is removed from the permeate zoneusing a liquid sweep stream. The permeate dissolves into the sweepstream and is conducted away by sweep stream flow in order to preventthe accumulation of permeate in the permeate zone. The sweep liquidpreferably has an affinity for, and is miscible with, the permeate. Inpervaporation, permeate is conducted away from the permeate zone as avapor. A vacuum, or reduced pressure, is maintained in the permeatezone, and the desired species or component in the feed stream willvaporize upon transfer across the membrane. In pervaporation, thedifference in vapor pressure between the feed stream in the retentatezone and the partial pressure of the permeate in the permeate zone leadsto the transfer of the desired species or component across the membrane.While the membrane has been described in terms of a flat sheet, theseparation process can employ a membrane in any workable configurationsuch as spiral-wound or hollow fibers.

Membrane separation should occur at a temperature less than thetemperature at which the membrane would be physically damaged ordecomposed. For hydrocarbon separations, the membrane temperature wouldrange from about 25° C. to about 500° C., and preferably from about 25°C. to about 250° C.

The method is useful for separating a desired species or component froma feedstream. In particular, the method is useful for separating adesired species or component from a hydrocarbon feed stream. In anembodiment, aromatics are separated from a hydrocarbon feedstream.

As used herein, the term “hydrocarbon” means an organic compound havinga predominantly hydrocarbon character. Accordingly, organic compoundscontaining one or more non-hydrocarbon radicals (e.g., sulfur or oxygen)would be within the scope of this definition. As used herein, the term“aromatic hydrocarbon” means a hydrocarbon-based organic compoundcontaining at least one aromatic ring. The rings may be fused, bridged,or a combination of fused and bridged. In a preferred embodiment, thearomatic species separated from the hydrocarbon feed contains one or twoaromatic rings. “Non-aromatic hydrocarbon” means a hydrocarbon-basedorganic compound having no aromatic cores. In an embodiment, thehydrocarbon feedstream has a boiling point in the range of about 25° C.to about 250° C., and contains aromatic and non-aromatic hydrocarbons.In a preferred embodiment, aromatic hydrocarbons are separated from anaphtha boiling in the range of about 25° C. to about 250° C. andcontaining aromatic and non-aromatic hydrocarbons. As used herein, theterm “naphtha” includes light naphthas boiling from about 25° C. toabout 100° C., intermediate naphthas boiling from about 100° C. to about160° C., and heavy naphthas boiling in the range of about 160° C. toabout 250° C. The term naphtha includes thermally cracked naphtha,catalytically cracked naphtha, and straight-run naphtha. Naphthaobtained from fluid catalytic cracking processes (“FCC”) areparticularly preferred due to their high aromatic content.

In a preferred embodiment, aromatics present in a naphtha feedstreampreferentially adsorb onto the layer of selective adsorption media onthe retentate side of a dynamic thin film polymer membrane. Pressure inthe retentate zone ranges from about atmospheric pressure to about 100psig. The temperature of the dynamic thin film polymer membrane wouldrange from about 25° C. to about 250° C. Aromatics separated from thenaphtha feedstream are conducted away from the permeate zone. Permeatezone pressure ranges from about atmospheric pressure to about 1.0 mm hg.

As discussed, it may be desirable to operate the membrane in theoperating region shown in FIG. 12. For conventional membranes, a thermalgradient would be present across the membrane from the highertemperature feed zone to the lower temperature permeate zone as a resultof the adiabatic cooling that would occur during separation. Dependingon the operating conditions, the thermal gradient can range from about10° C. to about 120° C. when aromatics are separated from hydrocarbon atpressures of about 2,000 psi to about 20,000 psi.

By using the membrane of the invention, it is possible to operate aseparation process so that the permeate zone is at a higher temperaturethan would be present in the case of adiabatic cooling. The membranes ofthe present invention, as set forth herein, are capable of conductingheat from the feed zone to the permeate zone. With permeate zoneheating, membrane separations can be operated at permeate zonetemperatures above those present in the conventional limit of adiabaticcooling. For example, the separation can be operated with the permeatezone at about the same temperature as the feed zone (i.e., isothermaloperation), or even at a higher temperature than the feed zone.

Although the present invention has been described in terms of specificembodiments, it is not so limited. Suitable alterations andmodifications for operation under specific conditions will be apparentto those skilled in the art. It is therefore intended that the followingclaims be interpreted as covering all such alterations and modificationsas fall within the true spirit and scope of the invention.

While not wishing to be bound by any theory or model, it is believedthat conventional membrane separation processes rely on a pressuregradient to establish a chemical potential for separation viaconcentration profile. The temperature gradient is controlled by thispressure gradient and an adiabatic flash cooling curve results. Thus thetemperature and pressure gradients are linked and not independent ofeach other. In a pervaporation membrane separation, this adiabatic flashcooling curve has a major impact on flux and selectivity performance.

The internally heated wafer assemblies of the invention provide adifferent process operating environment. The pressure gradient and thetemperature gradient that the membrane operates at can be independentlycontrolled. In the isothermal operating mode, the average membraneoperating temperature will be equal to the feed temperature which willbe equal to the permeate temperature. Typically this will result in anoperating temperature that is at least 40° C. higher than a typicaladiabatic operation.

Since the heat level of the heating medium can be selected independentof the process feed temperature, additional heating can be supplied tothe process. It is possible in this ‘Plus Heating Mode’ to operate themembrane temperature at a level higher than the process feed temperatureand additionally transfer plus heat to the feed/retentate. Typically fora polymeric membrane with a material operating limit of 200° C., thiswill result in an operating temperature that is at least 50° C. higherthan isothermal operation or +90° C. higher than conventional adiabaticoperation.

The commercial impact is to shift the membrane process costeffectiveness by 10 times to 100 times.

This new membrane module technology can be operated in any of the modesdescribed above: adiabatic (membrane average operating temperature lessthan the feed temperature), isothermal (membrane average operatingtemperature equal to the feed temperature) or plus heating (membraneaverage operating temperature higher than the feed temperature). Byselecting and controlling the average membrane operating temperature,the flux and selectivity can be adjusted to meet the performancerequirements of the process. This provides flexibility to makeadjustments as the feed composition changes or as the membrane ‘ages’and the performance shifts with ‘age’.

1. A method for separating desired components from a liquid feed streamcomprising: (a) conducting the liquid feed stream into a wafer assemblycomprising a wafer and a thin film polymer membrane mechanicallysupported by the wafer, the thin film polymer membrane being selectivefor permeation of a desired component and having an upstream side and adownstream side; (b) establishing a concentration gradient in thedesired component across the membrane in order to cause permeation ofthe desired component from the upstream side to the downstream side ofthe thin film polymer membrane and into a permeate zone in fluid contactwith the downstream side of the thin film polymer membrane, wherein thedownstream side is maintained at a second temperature above a firsttemperature, the first temperature being a characteristic of adiabaticcooling.
 2. The method of claim 1 further comprising: (a) conducting aretentate stream away from a retentate zone in fluid contact with theupstream side of the membrane, and (b) conducting a permeate streamcomprising the desired component away from the permeate zone.
 3. Themethod of claim 2 wherein the liquid comprises hydrocarbon and thedesired component comprises aromatics.
 4. The method of claim 1, furthercomprising (a) conducting the liquid feed stream in parallel into aplurality of wafer assemblies, each wafer assembly comprising at leastone wafer and at least one independently selected thin film polymermembrane mechanically supported by the wafer, each thin film polymermembrane being selective for permeation of the desired component or asecond desired component, and having an upstream side and a downstreamside; (b) establishing a concentration gradient in the desiredcomponent, across each independently selected thin film polymer membranein order to cause permeation of the desired component from the upstreamside to the downstream side of each thin film polymer membrane and intothe permeate zone; (c) conducting the retentate stream away from theretentate zone in fluid contact with the upstream side of each thin filmpolymer membrane; and (d) conducting the permeate stream comprising thedesired component away from the permeate zone; wherein the liquidcomprises hydrocarbon and the desired component comprises aromatics. 5.The method of claim 4 wherein the independently selected thin filmpolymer membranes comprise one or more of polyimide/aliphatic polyestercopolymers, crosslinked copolymers of aliphatic polyester diols anddianhydride, halogenated polyurethanes, diepoxide crosslinked/esterifiedpolyimide-aliphatic polyester copolymers, polyimide aliphatic polyestercopolymers, multi-block polymer comprising a urea prepolymer chainextended with a compatible second prepolymer, polycarbonate, highlyaromatic anisotropic polyurea/urethane membranes, highly aromaticpolyurea/urethane membranes, Isocyanurate crosslinked polyurethanemembranes, isocyanerate crosslinked polyurethane membranes, multi-blockpolymer comprising and imide or amide-acid prepolymer chain extendedwith a compatible second prepolymer, multi-block polymer comprising anoxazolidone prepolymer chain extended with a compatible secondprepolymer, multi-block polymer comprising a urea prepolymer chainextended with a compatible second prepolymer, multi-block, polymercomprising of first prepolymer made by combining epoxy with diamine,chain extended with a compatible second prepolymer, highly aromaticpolyurea/urethane, multi-block polymer comprising a first amide acidprepolymer, chain extended with a compatible second prepolymer, esterprepolymer, made by combining epoxy with polyester chain extended with acompatible second prepolymer, crosslinked polyester amide membranes,halogenated polyurethanes, saturated polyesters and crosslinkedmembranes, unsaturated polyesters and crosslinked membranes,polyimide/aliphatic polyester copolymers without pendent carboxylic acidgroups, polyphthalate carbonate membranes and polyarylate membranes. 6.The method of claim 4 wherein at least one wafer assembly furthercomprises at least one of a distribution weir, a screen, a supportfabric, alone or in combination.
 7. The method of claim 6 wherein themembrane support fabric selected from the group consisting of a Teflon,polyester, nylon, Nomex and Kevlar fabric.
 8. The method of claim 7wherein each independently selected thin film polymer membrane ismechanically supported by at least one rib member attached to the waferand wherein the rib member contains a bore therethrough.
 9. The methodof claim 8 wherein the second temperature is maintained by providing aheat transfer stream through at least one rib in order to heat the feedstream.
 10. The method of claim 4 further comprising suctioning thepermeate from said permeate zone.